A Long Term Evolution (LTE) wireless communication system is a new generation wireless network based on an Orthogonal Frequency Division Multiplexing (OFDM) technology, at a wireless side of which technologies such as Multiple Input Multiple Output (MIMO), high order modulation and corresponding frequency selection scheduling, power control and the like are adopted to cooperate, in order to achieve a higher system throughput and spectrum efficiency.
In an LTE system, the MIMO is regarded as an optimal technology to meet requirements of a user mean throughput and spectrum efficiency. In order to achieve the target, it is specified in the LTE system that, in different wireless channel environments, solutions including linear spatial pre-coding, beam forming, transmit diversity and the like can be self-adaptively selected through the MIMO technology.
The linear spatial pre-coding means that: when there are multiple transmitting antennas at a transmitting end, multiple data streams can be mapped to the multiple antennas through one linear pre-coding operation. A User Equipment (UE) generates a pre-coding vector according to an estimation of downlink spatial channel characteristics, and feeds it to an eNodeB side through an uplink control channel. The principle thereof is mainly that transmitting signals are located on a corresponding orthogonal basis of the channel matrix by pre-coding a matrix, and a main working mechanism thereof is that different data streams are transferred in a plurality of independent spatial channels to improve a peak rate of data transmission.
The main principle of the beam forming technology is to utilize a strong correlation among spatial channels and utilize an interference principle of a wave to generate a strongly directional radiation pattern, so that a main lobe of the radiation pattern is self-adaptively directed to a direction of a incoming wave of a user, as a result, a signal to noise ratio is increased and a system capacity or coverage is increased. The main principle of the transmit diversity is to utilize a weak correlation among the spatial channels and combine selectivity in terms of time/frequency to improve reliability of signal transmission based on a diversity gain, thereby improving the signal to noise ratio of a received signal.
The LTE system is configured with a plurality of UE Down Link (UE DL) transmission modes, different transmission modes can be selected to increase its own coverage and capacity, and each transmission mode respectively corresponds to a corresponding wireless transmission manner. In a region with a low signal to noise ratio, the transmit diversity technology and the beam forming technology can be utilized to effectively increase the signal to noise ratio of a received signal, so as to increase a transmission speed or a coverage; while in a region with a high signal to noise ratio, a transmission speed cannot be improved obviously any more by further increasing the signal to noise ratio, and the spatial multiplexing technology can be utilized to increase a data transmission speed without increasing a bandwidth.
Since there are the multiple UE DL transmission modes and a transmission technology corresponding to each transmission mode has pertinence, in a current LTE system, when a wireless environment is changed, a downlink transmission mode cannot be adjusted in real time and thus a resource utilization ratio is lower.